update atomics/color documentation

[wibjorn]

Link: http://localhost:1111/atomics/colors.html

The site has been lacking even moderate coverage of Atlas's expansive color classes. This PR adds some documentation for the most frequently used color atomics.

Testing

1. View page after running locally.

Additional information

[Optional]

Contributor checklist

• Did you update the description of this pull request with a review link and test steps?
• Did you submit a changeset? Changesets are required for all code changes.
• Does your pull request implement complex UI logic (js/ts)? Consider adding an integration test to test your user flow.
• Does your pull request add a new page to the documentation site? Add your new page for automated accessibility testing in /integration/tests/accessibility.

[changeset-bot]

🦋 Changeset detected

Latest commit: c80b597

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@microsoft/atlas-site	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR